client: Make aggregated to handle empty sequence

If begin == end (input sequence is empty) call to result complete
with -ENXIO and "has no requests to send" error
cache: decrease log level if cache is not enabled

There is no need to print error messages about cache is disabled
for lookup commands
client: Fixed read_latest policy

If there are no positive lookup result just complete request
with -ENOENT error
Merge pull request #370 from euroelessar/lts

Commits from master (lts)